This invention relates to a semiconductor wafer and a production method therefor and particularly, a semiconductor wafer obtained by forming a semiconductor thin film having a uniform resistivity distribution on a main surface of a large diameter semiconductor substrate and a production method therefor.
In company with recent miniaturization of an electronic device, not only has the use of semiconductor wafers each obtained by forming a silicon single crystal thin film on a main surface of a silicon single crystal substrate increased, but a more uniform resistivity distribution of the silicon single crystal thin film has also been required. The term xe2x80x9cuniform resistivity distributionxe2x80x9d used here, to be detailed, means that a resistivity distribution across the surface of the silicon single crystal thin film is uniform. Further, a larger diameter has also been demanded on a semiconductor wafer together with the uniform resistivity distribution. A horizontal, single wafer vapor phase growth apparatus has been mainly employed as an apparatus for growing a silicon single crystal thin film on a main surface of a silicon single crystal substrate keeping pace with use of a large diameter semiconductor wafer.
Description will be below given of a horizontal, single wafer vapor phase growth apparatus generally employed with reference to FIGS. 5 and 6, wherein FIG. 5 is a sectional view in a horizontal plane showing a conventional horizontal, single wafer vapor phase growth apparatus in a simplified manner and FIG. 6 is a vertical sectional view showing the apparatus in a simplified manner. As shown in FIGS. 5 and 6, in a conventional horizontal, single wafer vapor phase growth apparatus, a susceptor 14 on which a silicon single crystal substrate 12 is horizontally placed is disposed at the bottom of the middle portion of a transparent quartz glass reaction chamber 10 installed along a horizontal direction and the susceptor 14 is coupled with a rotation unit (not shown) through a rotary shaft 16.
Further, a gas inlet port 18 is provided at one end in a length direction of the reaction chamber 10 and a gas outlet port 20 is provided at the other end thereof. With this construction, a flow of a gas which is introduced through the gas inlet port 18 into the reaction chamber 10 and discharged through the gas outlet port 20 to the outside passes over a main surface of the silicon single crystal substrate 12 placed on the susceptor 14 almost along a length direction of the reaction chamber 10. Further, the gas inlet port 18 of the reaction chamber 10 is constructed of six inlet ports 18a to 18f spread in a width direction of the reaction chamber 10. Among the six inlet ports 18a to 18f, a pair of two inlet ports at the innermost side (hereinafter simply referred to as inner inlet ports) 18a and 18b are arranged in symmetry with respect to an imaginary central axis along a length direction of the reaction chamber 10, passing through the center of the main surface of the silicon single crystal substrate 12 on the susceptor 14, and this arrangement of the inner inlet ports 18a and 18b applies to not only a pair of two inlet ports at the outermost side (hereinafter simply referred to as outer inlet ports) 18e and 18f, but also a pair of two inlet ports each between one of the two inner inlet ports and the corresponding one of the two outer inlet ports (hereinafter simply referred to as middle inlet ports) in the same way.
To be more detailed, the inner inlet ports 18a and 18b are directed toward points in the vicinity of the center of the main surface of the silicon single crystal substrate 12 on an imaginary central axis along a width direction of the reaction chamber 10, passing through the center of the main surface of the silicon single crystal substrate 12 on the susceptor 14, and the outer inlet ports 18e and 18f are directed toward points in the vicinity of the outer periphery of the main surface of the silicon single crystal substrate 12 on the imaginary central axis line and the middle inlet ports 18c and 18d are directed toward points between the central portion and the outer peripheral portion of the main surface of the silicon single crystal substrate 12 on the imaginary central axis line.
Further, the six inlet ports 18a to 18f are all connected to a common gas pipe 22. The common gas pipe 22 are branched in three ways and the branches are connected to a gas source (not shown) of hydrogen (H2) gas as a carrier gas, a gas source (not shown) of a semiconductor raw material gas and a gas source (not shown) of a dopant gas through mass flow controllers MFC 24, 26 and 28, respectively, as gas flow rate regulators. Further, outside of the reaction chamber 10, an infrared radiation lamp 30, for example, as a heat source heating the silicon single crystal substrate 12 placed on the susceptor 14 is disposed and by supplying a power to the infrared radiation lamp 30, the main surface of the silicon single crystal substrate 12 is heated to a predetermined temperature. In addition, cooling means (not shown) for cooling the infrared radiation lamp 30 and an outer wall of the reaction chamber 10 is equipped. Then, description will be made of a method for forming a silicon single crystal thin film on the main surface of the silicon single crystal substrate 12 using the conventional horizontal, single wafer vapor growth apparatus shown in FIGS. 5 and 6.
First, the silicon single crystal substrate 12 is horizontally placed on the susceptor 14 of the reaction chamber 10. Following this, H2 gas is supplied into the reaction chamber 10 from the gas source of H2 gas through MFC 24, the common gas pipe 22 and through the six inlet ports 18a to 18f to replace the atmosphere in the reaction chamber 10 with hydrogen. Further, with the rotation device, the susceptor 14 is rotated through the rotary shaft 16 clockwise as shown by arrow marks of FIGS. 5 and 6 while the silicon single crystal substrate 12 is horizontally placed on the susceptor 14. Then, with the infrared radiation lamp 30, the silicon single crystal substrate 12 on the susceptor 14 is heated to raise a temperature of the main surface thereof to a predetermined one.
After doing so, the semiconductor raw material gas and the dopant gas are supplied into the reaction chamber 10 from the respective gas sources of the semiconductor raw material gas and the dopant gas through MFC 26 and 28, the common gas pipe 22 and the six inlet ports 18a to 18f. 
At this time, not only are flow rates of H2 gas as a carrier gas, the semiconductor raw material gas and the dopant gas controlled individually and precisely by MFC 24, 26 and 28, respectively, but the gases are mixed after the individual control and introduced into the reaction chamber 10 as a process gas having the raw material gas and the dopant gas of respective constant concentrations with almost no diffusion in a width direction through the six inlet ports 18a to 18f disposed in a width direction of the reaction chamber 10.
The process gas introduced into the reaction chamber 10 passes over the main surface of the silicon single crystal substrate 12 placed horizontally on the susceptor 14 rotating about the rotary shaft 16 as a center in one direction and in almost parallel to the main surface. During the passage over the main surface, a chemical reaction arises to grow the silicon single crystal thin film 32 in vapor phase on the main surface of the silicon single crystal substrate 12.
In a case where a silicon single crystal thin film 32 was formed on the main surface of the silicon single crystal substrate 12 using the conventional horizontal, single wafer vapor phase growth apparatus shown in FIGS. 5 and 6 as described above, and when the diameter of a silicon single crystal substrate 12 was 200 mm or less, a resistivity distribution along a diameter of the silicon single crystal thin film 32 formed on the main surface of the silicon single crystal substrate 12 was almost uniform. However, when a diameter of the silicon single crystal substrate 12 was larger than 200 mm, for example the diameter of as large as 300 mm, a conspicuous non-uniformity occurred in a resistivity distribution along a diameter direction of the silicon single crystal thin film 32. That is, a resistivity in the vicinity of the outer periphery of the silicon single crystal thin film 32 of a diameter of 300 mm was sharply reduced compared with the central portion other than an area in the vicinity of the outer periphery.
The sharp reduction in resistivity in the vicinity of the outer periphery of the silicon single crystal thin film 32 is estimated to be caused by the so-called auto-doping phenomenon. Here, the auto-doping phenomenon will be explained below:
When the silicon single crystal thin film 32 is grown in vapor phase on the main surface of the silicon single crystal substrate 12, an impurity added originally in the silicon single crystal substrate 12 is released into the reaction atmosphere through etching by H2 gas in the reaction atmosphere, occurring on a rear main surface of the silicon single crystal substrate 12 heated at a high temperature and works as a dopant gas. The dopant gas generated from the rear main surface of the silicon single crystal substrate 12 is migrated along the side surface of the silicon single crystal substrate, further comes onto the front main surface to be incorporated into the silicon single crystal thin film 32 during vapor phase growth. In such a way, since the dopant gas produced on the rear main surface of the silicon single crystal substrate 12 is supplied into the silicon single crystal thin film 32 in addition to a dopant gas introduced intentionally from a gas inlet port 18, an impurity more than necessary is added and thereby a resistivity of the silicon single crystal thin film 32 is forcibly reduced lower than a target value. Since a concentration of the dopant gas, around the silicon single crystal substrate, produced on the rear main surface, migrated along the side surface and coming onto the front main surface is highest at the outer peripheral portion and reduced toward the central portion, a sharp reduction in resistivity occurs in the vicinity of the outer periphery of the silicon single crystal thin film 32.
Such an auto-doping phenomenon occurs theoretically independent of a size of the silicon single crystal substrate 12. Actually, however, in a conventional case where a diameter of a silicon single crystal substrate 12 was less than 200 mm, reduction in resistivity in the vicinity of the outer periphery of a silicon single crystal thin film 32, caused by the auto-doping phenomenon was not conspicuous, so that a resistivity distribution across the silicon single crystal thin film 32 fell within an allowable range.
When this inventor used a silicon single crystal substrate 12 of 300 mm in diameter and a low resistivity to carry out vapor phase growth on a main surface thereof in order to respond to a recent demand for a semiconductor wafer of a large diameter, the inventor experienced a sharp reduction in resistivity in the vicinity of the outer periphery of the silicon single crystal thin film 32 due to the auto-doping phenomenon, with the result that a problem became obvious since there arose a conspicuous non-uniformity in a resistivity distribution along a diameter thereof.
It should be noted that it has been known, as means suppressing occurrence of the auto-doping phenomenon, that a film made of silicon nitride or silicon oxide is formed on a rear main surface of the silicon single crystal substrate 12. In this method, however, there is a fear that a film for prevention of an auto-doping phenomenon formed on the rear main surface of the silicon single crystal substrate 12 becomes a particle generation source and/or a metal contamination source, which entails a problem of a quality of the silicon single crystal thin film 32 formed on the front main surface of the silicon single crystal substrate 12 being degraded. In this method, in addition to an extra step of forming an auto-doping preventive film on the rear main surface of the silicon single crystal substrate 12, another extra step of removing the auto-doping preventive film after forming the auto-doping preventive film becomes necessary, which produces a problem of reduction in productivity and increase in production cost combined.
The invention has been made in light of the above described problems and it is accordingly an object of the invention to provide not only a semiconductor wafer obtained by forming a semiconductor thin film having a uniform resistivity distribution on a main surface of a large diameter silicon single crystal substrate of 300 mm or more in diameter, but a production method for a semiconductor wafer by which a semiconductor thin film having a uniform resistivity distribution is formed on a front main surface of a large diameter semiconductor single crystal substrate of 300 mm or more in diameter without forming an auto-doping preventive film on the rear main surface thereof. The above described task is achieved by a semiconductor wafer and a production method therefor relating to the invention described below:
That is, a semiconductor wafer relating to the invention is characterized by that the semiconductor wafer has a construction in which a semiconductor thin film of 8% or less in resistivity distribution along a diameter is formed on a p-type semiconductor single crystal substrate of a diameter ranging from 300 mm to 400 mm, both limits being included, and a resistivity ranging from 0.01 xcexa9xc2x7cm to 0.02 xcexa9xc2x7cm, both limits being included. Here, a value representing a resistivity distribution along a diameter of a semiconductor thin film, that is, 8% or less is calculated by the following formula:
(Maximum resistivityxe2x88x92Minimum resistivity)/average resistivity over all measurement pointsxe2x80x83xe2x80x83(1)
In such a manner, in a semiconductor wafer relating to the invention, a semiconductor thin film of 8% or less in resistivity distribution along a diameter is formed on a main surface even of a p-type semiconductor single crystal substrate as large as from 300 mm to 400 mm, both limits being included, in diameter and as low as from 0.01 xcexa9xc2x7cm to 0.02 xcexa9xc2x7cm, both limits being included, in resistivity, and thereby a large diameter and a uniform resistivity distribution as characteristics of a recent semiconductor wafer are both achieved, which contributes largely to increase in throughput and yield of semiconductor chips in production.
It is preferable that in a semiconductor wafer relating to the invention, a resistivity distribution along a diameter of a semiconductor thin film formed on a main surface of a p-type semiconductor single crystal substrate is within xc2x14% or less. Here, a value representing a resistivity distribution along a diameter of a semiconductor thin film, that is, xc2x14% or less is calculated by the following formula:
(Maximum resistivityxe2x88x92Minimum resistivity)/(Maximum resistivity+Minimum resistivity)xe2x80x83xe2x80x83(2)
In this case, uniformity in resistivity distribution required for a recent semiconductor wafer is achieved with a high accuracy, thus further contributing to increase in yield of semiconductor chips in production.
Further, in a semiconductor wafer relating to the invention, a diameter of the semiconductor single crystal substrate is preferably 300 mm. At the present stage, since a semiconductor single crystal substrate with a diameter up to 300 mm can be produced in a stable manner with high quality, it is practically enjoyed to an full extent that a resistivity distribution of a semiconductor thin film along a diameter is achieved with uniformity of 8% or less (in a case of calculation with the above described formula (1)) or within xc2x14% or less (in a case of calculation with the above described formula (2)) on a main surface of a semiconductor single crystal substrate as low as from 0.01 xcexa9xc2x7cm to 0.02 xcexa9xc2x7cm, both limits being included, in resistivity.
Further, it is preferable that a semiconductor single crystal substrate is a silicon single crystal substrate and a semiconductor thin film is a silicon single crystal thin film. That is, since a large diameter and a uniform resistivity distribution as characteristics of a silicon single crystal wafer, which is a main stream of currently used semiconductor wafers, are both achieved, there arises expectation of a wide application of the silicon single crystal wafer in various aspects in fabrication of semiconductor devices.
Further, in a production method for a semiconductor wafer relating to the invention, a semiconductor raw material gas is supplied through a plurality of gas inlet ports disposed in a width direction of the reaction chamber onto a main surface of a semiconductor single crystal substrate rotating in a reaction chamber in one direction in almost parallel to the main surface thereof to grow a semiconductor thin film on the main surface thereof in vapor phase and a dopant gas is supplied from gas inlet ports in the inner side among the plurality of gas inlet ports.
In such a manner, in a production method of a semiconductor wafer relating to the invention, a semiconductor raw material gas is supplied through the plurality of gas inlet ports disposed in a width direction of the reaction chamber onto a main surface of a semiconductor single crystal substrate in one direction in almost parallel to the main surface thereof and a dopant gas is supplied from gas inlet ports in the inner side among the plurality of gas inlet ports, that is, without supplying the dopant gas from gas inlet ports in the outer side among the plurality of gas inlet ports, with the result that a concentration of the dopant gas supplied into the vicinity of the outer periphery of the main surface of a semiconductor single crystal substrate is lower than that supplied into the central portion other than an area in the vicinity of the outer periphery on a relative basis. In this situation, however, a dopant gas produced on a rear main surface of the semiconductor single crystal substrate, migrating along the side surface thereof and coming onto the front main surface thereof is supplied in the vicinity of the outer periphery thereof by the auto-doping phenomenon. For this reason, a dopant gas supplied from the gas inlet ports and a dopant gas supplied by the auto-doping phenomenon are combined and thereby, a concentration of the combined dopant gas supplied onto the front main surface of the semiconductor single crystal substrate can be almost uniform across the whole of the front main surface. As a result, a resistivity distribution along a diameter of the semiconductor thin film grown in vapor phase on the front main surface of the semiconductor single crystal substrate can be more uniform.
Further, in a production method for a semiconductor wafer relating to the invention, the plurality of gas inlet ports are preferably composed of three kinds: an inner inlet port disposed at the innermost side in a width direction of a reaction chamber, an outer inlet port disposed at the outermost side in the width direction thereof and a middle inlet ports disposed between the inner inlet port and the outer inlet port and gas inlet ports disposed in the inner side among the plurality of gas inlet ports include the inner inlet port and the middle inlet port.
In such a manner, in a production method for a semiconductor wafer relating to the invention, the plurality of gas inlet ports include the three kinds of the inner gas inlet port, the outer gas inlet port and the middle gas inlet port and, on an imaginary central axis along a width direction of the reaction chamber, passing through the center of the main surface of the semiconductor single crystal substrate, a semiconductor raw material gas is supplied onto an area in the vicinity of the center of the main surface of the semiconductor single crystal substrate from the inner gas inlet port, onto an area in the vicinity of the outer periphery thereof from the outer gas inlet port and onto an intermediate area between the area in the vicinity of the center and the area in the vicinity of the outer periphery from the middle gas inlet port, while a dopant gas is not supplied from the outer gas inlet port but from the inner and middle gas inlet ports. In this situation, since while a concentration of a dopant gas supplied in the vicinity of the outer periphery of the main surface of the semiconductor single crystal substrate is lower than those of the dopant gas supplied to the area in the vicinity of the central portion and the intermediate area on a relative basis, an additional dopant gas produced by the auto-doping phenomenon is supplied to the area in the vicinity of the outer periphery, therefore a concentration of the combined dopant gas supplied to across all the main surface of the semiconductor substrate is almost uniform. Accordingly, a resistivity distribution along a diameter of the semiconductor thin film grown in vapor phase on the main surface of the semiconductor single crystal substrate becomes more uniform with no need to provide an extra step of forming an auto-doping protective film on the rear main surface thereof.
It should be noted that while description is made of the case where among the plurality of gas inlet ports disposed in a width direction of a reaction chamber, two kinds of inner and middle gas inlet ports are provided as gas inlet ports disposed in the inner side of the plurality of gas inlet ports for supply of a dopant gas, three or more kinds of gas inlet ports can also be provided as the gas inlet ports disposed in the inner side thereof for supply of a dopant gas according to a size of a semiconductor single crystal substrate.
Further, in a production method for a semiconductor wafer relating to the invention, it is further preferable that dopant gas rates supplied from the inner and middle inlet ports are individually controlled.
In such a manner, since in a production method for a semiconductor wafer, dopant gas rates supplied onto the area in the vicinity of the center and the intermediate area of a main surface of a semiconductor single crystal substrate other than the area in the vicinity of the outer periphery thereof are individually controlled on an imaginary central axis along a width direction of the reaction chamber, passing through the center of the main surface of the semiconductor single crystal substrate, therefore concentrations of a dopant gas supplied onto the area in the vicinity of the center and the intermediate area can be closer in magnitude to each other, resulting in more uniform resistivity distribution along a diameter of a semiconductor thin film grown in vapor phase on the main surface of a semiconductor single crystal substrate.
It should be noted that in a production method for a semiconductor wafer relating to the invention, it is preferable that as a semiconductor single crystal substrate, there is used a p-type semiconductor single crystal substrate of a diameter ranging from 300 mm to 400 mm, both limits being included, and especially a diameter of 300 mm and of a resistivity ranging from 0.01 xcexa9xc2x7cm to 0.02 xcexa9xc2x7cm, both limits being included.
That is, since in a case where a semiconductor single crystal substrate is of a diameter in the range of from 300 mm to 400 mm, both limits being included, and among them, especially, a diameter of 300 mm, a semiconductor single crystal substrate of which can be produced in a stable manner with high quality at the present stage, reduction in resistivity in the vicinity of the outer periphery of a semiconductor single crystal thin film caused by the auto-doping phenomenon becomes conspicuous, therefore stoppage of dopant gas supply onto an area in the vicinity of the outer periphery from a gas inlet port exerts practically a sufficient influence to make a resistivity distribution along a diameter of the semiconductor thin film uniform.
It should be noted that in a production method for a semiconductor wafer relating to the invention, a diameter of a semiconductor single crystal substrate is not limited to the range of from 300 mm to 400 mm, both limits being included, but a diameter beyond 400 mm thereof can be still used in the production method. In this case, as described above, a measure is conceived in which three or more kinds of gas inlet ports are provided as gas inlet ports in the inner side for supply of a dopant gas.
Further, in a case where a semiconductor single crystal substrate of a low resistivity lower than 0.01 xcexa9xc2x7cm is used, since an influence of the auto-doping phenomenon increases and reduction in resistivity in the vicinity of the outer periphery of a semiconductor single crystal thin film caused by an increased influence is too sharp, simple stoppage of supply of a dopant gas onto area in the vicinity of the outer periphery of the semiconductor single crystal thin film from a gas inlet port is hard to exert a sufficient effect to make a resistivity distribution along a diameter of the semiconductor single crystal thin film uniform. On the other hand, in a case where a high resistivity semiconductor single crystal substrate of a resistivity higher than 0.02 xcexa9xc2x7cm is used, since an influence of the auto-doping phenomenon decreases and reduction in resistivity in the vicinity of the outer periphery of a semiconductor single crystal thin film caused by the influence thereof becomes small, there arises no need for stoppage of supply of a dopant gas on to the area in the vicinity of the outer periphery from a gas inlet port, but depending on circumstances, stoppage of supply of a dopant gas onto the area in the vicinity of the outer periphery, to the contrary, has a risk to induce non-uniformity in resistivity distribution across all the semiconductor single crystal thin film. Therefore, in a case of a resistivity of a semiconductor single crystal substrate ranging from 0.01 xcexa9xc2x7cm to 0.02 xcexa9xc2x7cm, both limits being included, stoppage of supply of a dopant gas onto an area in the vicinity of the outer periphery of the substrate from a gas inlet port works most effectively to make a resistivity distribution along a diameter of a semiconductor thin film uniform.
Further, in a production method for a semiconductor wafer relating to the invention, it is preferable that a semiconductor single crystal substrate is a silicon single crystal substrate and a semiconductor thin film is a silicon single crystal thin film. That is, a large diameter and a uniform resistivity distribution of a silicon single crystal wafer that is currently a main stream of semiconductor wafers are both achieved and thereby, a wide application of the silicon single crystal wafer in various aspects are expected in fabrication of semiconductor devices.